Surface treatment of inorganic fillers

ABSTRACT

This invention relates to a method of surface treating particulate inorganic fillers with a surface-treating agent which is an equilibrated reaction mixture consisting essentially of R 2  SiO 2/2  units, RSiO 3/2  units and CH 3  O 1/2  radicals wherein the mixture contains A moles of R 2  SiO 2/2  units per mole of RSiO 3/2  units and B moles of CH 3  O 1/2  radicals, A having an average value of from 0.5 to 10 and B having an average value of from 3 to 6, the value of B being related to A such that when A=0.5, B=6 and when A=10, B=3, and R being a hydrocarbon radical of from 1 to 10 inclusive carbon atoms or a haloalkyl radical of from 1 to 10 inclusive carbon atoms. Reinforcing silica fillers, surface-treated with such equilibrated reaction mixtures can be compounded with polydiorganosiloxanes curable to elastomers and cured to obtain silicone elastomers possessing high optical clarity and physical properties which make the cured elastomer uniquely suitable for use as prosthetic devices for use on or within the body.

This invention relates to a method of surface treating particulateinorganic fillers with an equilibrated reaction mixture composed of aparticular ratio of siloxane units bearing methoxy radicals, to thesurface-treated fillers themselves and to polysiloxane compositions andcured silicone elastomer articles of manufacture containing suchfillers.

BACKGROUND OF THE INVENTION

Various types of organosilanes and polyorganosiloxanes such ashydroxyl-endblocked polydimethylsiloxanes have been employed to surfacetreat the surfaces of particulate inorganic fillers, particularlyreinforcing silica fillers, to render the surfaces of the fillershydrophobic. As a result the handling properties of the uncuredelastomer (filler-gum) composition are improved and the tendency for thecomposition to crepe harden is reduced. The physical properties such astensile strength of the cured elastomers may also be improved.

For example, U.S. Pat. No. 2,954,357 (Fekete, issued Sept. 27, 1960)teaches the use of certain dihydrocarbon polysiloxane oils having ahydrocarbon substituent to silicon aton ratio of 1.6 to 2.0, preferablyfrom 1.889 to 2.0 and an average of from 1 to 2 preferably from 1 to1.5, lower alkoxy groups, per terminal silicon atom to improve thebin-aging characteristics of filler-containing polydiorganosiloxane gumcompositions. Ethoxy radicals appear to be the alkoxy radical of choiceand the polysiloxane oils used in these compositions contain at least 4and as much as 35 or more dihydrocarbonsiloxy units per molecule andhave molecular weights of from about 400 to 2700, preferably from about600 to 1500. The method of preparing such polysiloxane oils is said tobe taught in U.S. Pat. No. 2,909,549 (Bailey, issued Oct. 20, 1959)which teaches that alkoxy-endblocked polysiloxanes can be produced byequilibrating, among other reactants, monoalkyltrialkoxysilanes ordialkyldialkoxysilanes with cyclic polysiloxanes in the presence of abasic catalyst.

U.S. Pat. No. 3,024,126 (Brown, issued Mar. 6, 1962) teaches thatreinforcing silica fillers can be surface-treated with certain hydroxyor alkoxy functional organosilanes in an organic solvent in the presenceof certain basic catalysts. The Brown Patent teaches the use of certainlower molecular weight monoalkoxy- and dialkoxy-endblockeddihydrocarbonsiloxanes as surface treating agents, but teaches thatthere should not be more than three and preferably no more than onealiphatic, monovalent hydrocarbon radical per siloxane unit. If morethan about three di-aliphatic-monovalent-hydrocarbon-radical-substitutedsilicon atoms in any siloxane molecule, the Brown Patent teaches thatthe effectiveness of the resulting treated silica will be substantiallyreduced.

U.S. Pat. No. 3,979,546 (Lewis, issued Sept. 7, 1976) teaches thesurfaces of inorganic materials can be rendered hydrophobic bycontacting them with alpha-alkoxy-omegasiloxanols containing one alkoxygroup per molecule which are obtained from the reaction of cyclicsiloxanes which alcohols under mild reaction conditions. Whilereasonably rapid conversion to product is obtained fromhexamethylcyclotrisiloxane, Examples 3 and 4 indicate that conversion ofoctamethylcyclotetrasiloxane and decamethylcyclopentasiloxane to thecorresponding alpha-alkoxy, omega-siloxanol useful as a treating agentwas rather slow.

U.S. Pat. No. 2,927,909 (Lyons, et al., issued Mar. 8, 1960) teaches theuse of (A) 65-85 parts by weight of a copolymer of 65-85 mole percent ofmonomethylsiloxane, 15-30 mole percent of dimethylsiloxane and no morethan 5 mole percent of trimethylsiloxane which has from 1-12 weightpercent silicon-bonded methoxy radicals and (B) from 15-35 parts byweight of monopropylsiloxane containing from 15 to 60% by weightsilicon-bonded ethoxy radicals as a masonry water repellent. Nothing istaught concerning the use of component (A) and/or (B) to surface treatinorganic particulate fillers.

U.S. Pat. No. 2,706,724 (Bass, issued Apr. 19, 1955) teaches the use ofa partial hydrolyzate of an alkoxylated (20-50 weight percent alkoxyradicals) mixture of by-product chlorosilicon compounds obtained fromthe reaction of CH₃ Cl and Si as a water repellent treatment formasonry. Nothing is taught concerning the use of the compositionsdescribed in the Bass Patent for surface-treating inorganic particulatefillers.

SUMMARY OF THE INVENTION

It has been discovered that a unique equilibrated reaction mixtureconsisting of a mixture of certain methoxy-functional organosilanes andorganosiloxanes having an overall average molecular weight of less than500 can be employed to surface-treat particulate inorganic fillers,particularly reinforcing siliceous fillers, at room temperature orabove. The equilibrated reaction mixture is preferably obtained byequilibrating a mixture of RSi(OCH₃)₃ with a mixture of cyclicdiorganosiloxanes consisting predominantly of readily commerciallyavailable liquid diorganocyclotetrasiloxanes which tend to be much lessreactive to ring opening reactions than are thediorganocyclotrisiloxanes such as hexamethylcyclotrisiloxane which is awaxy solid at room temperature.

Inorganic particulate fillers, particularly reinforcing silica fillers,can be used to produce compositions curable to silicone elastomers whichare easier to handle and extrude in the uncured state. The uncuredcompositions can be stored for periods of several weeks to severalmonths without developing a sufficient amount of structure build-up tobecome crepe-hardened. Furthermore, the equilibrated reaction mixturesemployed in the method of the present invention enable one to producesurface-treated, hydrophobic reinforcing silica fillers which can beused to produce cured silicone elastomers which are optically clear andpossess tensile stength, elongation at break, durometer and tear valueswhich make cured elastomers containing such treated fillers uniquelysuitable for articles such as rubber tubing, windshield interlayers, andwhen the cured elastomer is biocompatible, for use as elastomericprosthetic devices such as eye contact lenses, implantable devices suchas mammary implants, finger joints and other devices designed for use onor within the body.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of surface treating aparticulate inorganic filler which comprises the steps of (A) contacting100 parts by weight of a particulate inorganic filler with a surfacetreating agent comprising at least one component which is anequilibrated reaction mixture consisting essentially of R₂ SiO_(2/2)units, RSiO_(3/2) units and CH₃ O_(1/2) radicals, there being A moles ofR₂ SiO_(2/2) units per mole of RSiO_(3/2) units present in said mixtureand B moles of said CH₃ O_(1/2) radicals, said A having an average valueof from 0.5 to 10 and B having an average value of from 3 to 6, thevalue of B being related to A such that when A=0.5, B=6 and when A=10,B=3, and wherein R is selected from the group consisting of hydrocarbonradicals of from 1 to 10 inclusive carbon atoms and haloalkyl radicalsof from 1 to 10 inclusive carbon atoms, there being at least 5 parts byweight of said equilibrated reaction mixture based on the total weightof R₂ SiO_(2/2) and RSiO_(3/2) units present in the mixture per 100parts by weight of said filler, and (B) maintaining saidsurface-treating agent in contact with said filler for a sufficientamount of time to obtain a hydrophobic, surface-treated particulateinorganic filler.

This invention also relates to the surface-treated fillers themselvesand to compositions curable to silicone elastomers which containinorganic particulate fillers surface treated by the above method. Thisinvention also relates to cured silicone elastomers containing inorganicparticulate fillers which are surface treated by the above method andmore particularly to cured silicone elastomers in the form of prostheticdevices.

Examples of inorganic particulate fillers useful in the presentinvention can be any of a number of well-known fillers used to formulatesilicone elastomers such as finely divided pure silicas such as thoseobtained by the flame hydrolysis of silanes sold under the trademarksCAB-O-SIL® and AEROSIL®, precipitated silica fillers prepared fromsodium silicate or alkyl orthosilicates, diatomaceous silica, aluminumsilicate, calcium carbonate, zinc oxide, zirconium silicate, titaniumdioxide, barium sulfate, aluminum oxide, powdered quartz and the like.Preferably, reinforcing silia fillers such as fume silica orprecipitated silica having B.E.T. (Brunauer, Emmett and Teller) Methodsurface areas of at least 50 square meters per gram and preferablygreater than 200 square meters per gram are used.

The equilibrated reaction mixture consists essentially of the product ofan equilibrium reaction between a source of R₂ SiO_(2/2) units which ispreferably at least one cyclic polydiorganosiloxane of the unit formula(R₁ SiO)_(x) wherein x has a value of from 3 to 7 and an organosilane ofthe formula RSi(OCH₃)₃. Preferably, the source of R₂ SiO_(2/2) units isa mixture of cyclic polydiorganosiloxanes of the unit formula (R₂SiO)_(x) wherein at least 70 weight percent of the mixture is composedof cyclic polydiorganosiloxanes wherein x=4 since, as is well known inthe art, such a mixture is readily obtained from the hydrolysis ofdimethyldichlorosilanes. The use of a methoxy-functional organosiloxaneis preferred because the methoxy radical rapidly reacts with, forexample, hydroxyl groups present on the surface of inorganic fillers,especially those on siliceous fillers, to produce a low molecular weightalcohol (methanol) and also has the advantage of providing the highestlevel of treatment efficiency due to the low molecular weight of themethoxy radical relative to the remainder of the siloxane units presentin the reaction mixture. Each R is selected from the group consisting ofhydrocarbon radicals of from 1 to 10 inclusive carbon atoms such asmethyl, ethyl, propyl, hexyl, cyclohexyl, phenyl, benzyl, vinyl, allyland naphthyl, haloalkyl radicals of from 1 to 10 inclusive carbon atomssuch as chloromethyl, 3,3,3-trifluoropropyl and CF₃ C₉ H₁₈ --, with Rpreferably being methyl, vinyl, phenyl and 3,3,3-trifluoropropylradicals since organosilanes and organosiloxanes bearing those radicalsare commonly available and is, more preferably, methyl and vinylradicals. Each R radical present in the equilibrated reaction mixturecan be the same or different, but, preferably, more than 50 mole percentof the R radicals, and, more preferably, at least 90 mole percent of theR radicals present in the equilibrated reaction mixture are methylradicals since materials bearing such radicals are commerciallyavailable materials.

A sufficient amount of the source of R₂ SiO_(2/2) units andorganosilioxane, RSi(OCH₃)₃ to result in a molar ratio of R₂ SiO_(2/2)units to RSiO_(3/2) units (R₂ SiO_(2/2) :RSiO_(3/2)) in the range of0.5:1 to 10:1 are equilibrated at a temperature from about 40° C. to200° C. for a period of several minutes to several days in the presenceof an acidic or basic catalyst substantially in the absence of water (orat least provided with a well known means to remove any water that mightbe generated during the equilibration reaction, e.g., by azeotropicallyremoving the water). Equilibration techniques for preparing suchmixtures are well known in the art and further details concerning thepreparation of such mixtures will be given in the following Examples.Generally, a basic catalyst such as potassium silanolate present in aratio of 1 potassium atom per 1000 to 5000 silicon atoms present in themixture gave equilibrated reaction mixtures within less than about 3hours at 95°-120° C. The progress of the equilibration reaction isfollowed by observing the eluted fractions through the use of gas-liquidchromatographic techniques. The reaction mixture is considered to be"equilibrated" for the purposes of this invention when the elutedfractions found in a gas-liquid chromatogram of the reaction mixtureshows that the composition of the reaction mixture attained relativelyconstant composition. After equilibration, the overall composition ofthe equilibrated mixture "consists essentially" of R₂ SiO_(2/2) units,RSiO_(3/2) units and CH₃ O_(1/2) radicals, there being A moles of R₂SiO_(2/2) units per mole of RSiO_(3/2) units present in said mixture andB moles of said CH₃ O_(1/2) radicals, said A having an average value of0.5 to 10 and B having an average value of from 3 to 6, the value of Bis dependent upon the value of A with B=6 when A=0.5 and B=3 when A=10.

The lowest average molecular weight equilibrated reaction mixtures areobtained when 0.5 moles of R₂ SiO_(2/2) units is equilibrated with 1mole of RSi(OCH₃)₃ and that ratio is about the lower limit for obtainingefficient filler surface-treatment. The highest average molecular weightequilibrated reaction mixtures are obtained when 10 moles of R₂SiO_(2/2) units are equilibrated with 1 mole of RSi(OCH₃)₃ units. Thisratio was deemed to be the upper limit for efficient surface-treatmentbecause as the molar ratio of R₂ SiO_(2/2) :RSiO_(3/2) of theequilibrated reaction mixture was increased, longer periods of time wererequired to surface-treat silica filler particles at room temperature asevidenced (see the following Examples) by the amount of filler agingtime necessary to obtain ultimate physical properties when curedsilicone elastomers were prepared using silica fillers treated inaccordance with the method of the present invention. It was unexpectedlyfound that the most desirable balance of uncured silicone elastomerplasticity and handling properties coupled with high optical clarity andphysical properties such as a combination of a high tensile strengthwith relatively high elongation and Die B tear values was obtained whenthe reaction mixtures employed to surface treat the silica filler hadmolar ratios of R₂ SiO_(2/2) :RSiO_(3/2) in the range of 0.75 to 4 andthe best overall balance of properties was obtained when the ratio wasbetween 0.9 and 1.1. This is unexpected since a 1:1 molar ratioindicates that about 50 mole percent of the surface-treating agent iscomposed of RSiO_(3/2) units. It has been more common to employsurface-treating agents for siliceous and other fillers which arepredominantly composed of R₂ SiO_(2/2) units or triorganosiloxy unitssuch as those derived from hexamethyldisilazane. The latter agents havea higher number of R radicals per siloxane unit and would be expected tomore efficiently surface-treat and render the surface of fillershydrophobic than would RSiO_(3/2) units.

Examples of sources of R₂ SiO_(2/2) units are the previously mentionedcyclic polysiloxanes which are preferred because they add no otherpotentially hydrolyzable groups to the reaction mixture. Morespecifically, cyclic polydimethyl siloxane such ashexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, [(C₆ H₅)₂ SiO]₃,1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane,1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)-cyclotrisiloxane,mixtures of cyclic ploydiorganosiloxanes, and, when an economical sourceof R₂ SiO_(2/2) units is desired, especially when R is a methyl radical,preferably a mixture of cyclic polydimethylisiloxanes of the unitformula (R₂ SiO)_(x) is used wherein at least 70 weight percent of themixture is composed of cyclic polydiorganosiloxanes wherein x=4. Theterm "consisting essentially of" with reference to the equilibratedreaction mixtures useful in the method of the present invention isintended to mean that a small amount of other siloxane units, in anyevent no more than 5 mole percent of the total siloxane units present inthe equilibrated reaction mixture, can be units such as R₃ SiO₀.5 thatcould be present if a low molecular weight triorganosiloxy-endblockedpolydiorganosiloxane fluid such as (CH₃)₃ SiO[(CH₃)₂ SiO]_(y) Si(CH₃)₃where y has an average value of from 1 to 10 were used as a source forthe R₂ SiO_(2/2) units, however the previously mentioned cyclicpolydiorganosiloxanes are preferred.

Specific examples of RSi(OCH₃)₃ are methyltrimethoxysilane,ethyltrimethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane,allyltrimethoxysilane, chloromethyltrimethoxysilane and3,3,3-trifluoropropyltrimethoxysilane, with methyltrimethoxysilane andvinyltrimethoxysilane being preferred.

One advantage of using the equilibrated reaction mixtures of the presentinvention is that if necessary, the equilibration catalyst is simplyremoved from the equilibrated reaction mixture and the reaction mixtureis stored in the absence of moisture until it is used, as is, to surfacetreat a particulate inorganic solid. There is no need to use a strippingprocess to remove any of the components of the mixture before use.

The inorganic particulate filler can be surface treated with the aboveequilibrated reaction mixtures themselves simply by bringing theequilibrated reaction mixture into intimate contact with the filleritself or by blending the filler to be treated into at least onepolydiorganosiloxane and thereafter introducing an amount of theequilibrated reaction mixture into the filler-polydiorganosiloxanecomposition. Generally, about 5 parts by weight of the equilibratedreaction mixture (calculated as a total weight of R₂ SiO_(2/2) andRSiO_(3/2)) per 100 parts by weight of the filler to be treated isnecessary to provide the filler with an adequate level ofsurface-treatment to enable it to become surface treated and hydrophobicand to improve the physical properties of the silicone elastomercompositions into which it is added. While there is no critical upperlimit for the amount of equilibrated reaction mixture (calculated as atotoal weight of R₂ SiO_(2/2) and RSiO_(3/2)) used to surface treat thefiller, the use of a sufficient amount of equilibrated reaction mixtureto provide more than about 50 parts by weight of total R₂ SiO_(2/2) andRSiO_(3/2) units per 100 parts by weight of filler may be wasteful andcan have a detrimental effect on the properties of cured elastomerscontaining such fillers. The actual surface treating agent employed inthe method of the present invention may include more than just theequilibrated reaction mixture as will be shown in the followingExamples. For example, a basic catalyst such as ammonium hydroxide orammonium carbonate can be used to improve the filler surface treatmentrate. The equilibrated reaction mixture can also be dissolved in anorganic solvent such as methanol or toluene, which optionally includes abasic catalyst, and used to surface treat the filler in a solventslurry. The fillers are then aged for a sufficient amount of time atroom temperature up to about 100° C., preferably at room temperature,until the fillers become hydrophobic and surface treated, generally fromabout 15 minutes to several weeks, preferably from 15 minutes to 24hours and most preferably from 15 minutes to 4 hours. Hydrophobicreinforcing silica fillers prepared by precipitating alkyl silicates ofthe type described in U.S. Pat. No. 4,344,800 (Lutz, issued Aug. 17,1982) can be produced by substituting the equilibrated reaction mixturesof the present invention in place of the hydrophobe agents described inthe Lutz Patent and that patent is hereby incorporated by reference toteach another method by which the method of the present invention can bepracticed. Other methods of surface treating particulate fillers inaccordance with the method of the present invention will be evident tothose skilled in the art. Several silica fillers prepared bysubstituting the equilibrated reaction mixtures of the present inventionfor the hydrophobe agents described in the Lutz Patent were found tohave BET surface areas of from 290 to 330 m² /g.

The surface-treated fillers obtained by the above method can then becompounded into polydiorganosiloxanes to form compositions curable tosilicone elastomers using polydiorganosiloxanes and compounding methodswhich will be familiar to those skilled in the art.Polydiorganosiloxanes useful in preparing compositions curable tosilicone elastomers are well known and the nature of thepolydiorganosiloxanes into which surface-treated inorganic particulatefillers, particularly surface treated reinforcing siliceous fillers, ofthe present invention are compounded forms no part of the presentinvention. Generally, the compositions curable to silicone elastomerscomprise from 50 to 97.5 parts by weight of at least onepolydiorganosiloxane and from 2.5 to 50 parts by weight ofsurface-treated particulate inorganic filler. One type of curablecomposition employing surface-treated silica fillers is described inpending U.S. patent application Ser. No. 309,302, filed on Oct. 7, 1981(now U.S. Pat. No. 4,418,165) in the names of K. E. Polmanteer and H. L.Chapman entitled "Optically Clear Silicone Compositions Curable toElastomers" which is assigned to the same assignee as is the presentinvention. U.S. Ser. No. 309,302 above is hereby incorporated byreference to teach polydiorganosiloxanes which can be used incombination with the surface-treated silica fillers of the presentinvention to prepare cured silicone elastomers possessing high opticalclarity, to teach methods for incorporating such fillers into thepolydiorganosiloxanes and to teach methods for curing such compositions.Other examples of patents describing polydiorganosiloxanes curable tosilicone elastomers are those patents listed in U.S. Pat. No. 3,677,877(Metevia, et al., issued July 18, 1972) which are hereby incorporated byreference to teach such polydiorganosiloxanes, curable compositionscontaining such polydiorganosiloxanes and methods of curing the same.

Cured silicone elastomers containing surface-treated inorganicparticulate fillers of the present invention are useful in variousapplications such as molded articles in the form of hoses, gaskets and,face masks. Cured polydimethylsiloxane elastomers containing reinforcingsiliceous fillers of the present invention, particularly those made fromthe alkaline hydrolysis of methyl orthosilicate, were found to possesshigh optical clarity in addition to a combination of high tensilestrength, high elongation and reasonably high durometer and Die B tearvalues which makes such cured elastomers highly desirable for use asprosthetic devices for use or in combination with the body such as eyecontact lenses, implantable devices such as finger joints, mammaryprostheses, chin implants and the like.

The following definitions shall apply in the Examples below:

"Me"--Methyl.

"Vi"--Vinyl.

"MTMS"--Methyltrimethoxysilane

"Mixed Cyclics"--A mixture of cyclic polydimethylsiloxanes of the unitformula [(CH₃)₂ SiO]_(x) where x has an integral value of from 3 to 7and wherein about 78 weight percent of the mixture is composed of[(CH₃)₂ SiO]₄.

"Conc. Ammonium Hydroxide"--Concentrated aqueous ammonium hydroxidehaving approximately 28% NH₃ content and a density of approximately 0.9g/ml where "g" is grams and "ml" is milliliters.

"NH₃ /Methanol Solution"--Solution of ammonia gas in methanol containingapproximately 0.11 g NH₃ /ml, density approximately 0.8 g/ml.

"MOS"--Methyl orthosilicate (density approximately 1.014 g/ml).

"Catalyst A"--Hexane solution of a potassium silanolate catalyst havinga basic neutralization equivalent of 2700 g/equivalent of potassium.

"Catalyst B"--Ion exchange resin in bead form bearing surface-bondedsulfonic acid groups which is sold under the trademark "AMBERLYST®15" byRohm and Haas Company, Inc., Philadelphia, PA.

"Catalyst C"--Potassium silanolate catalyst having a neutralizationequivalent of 425 g/equivalent of potassium.

"Gum A"--A dimethylvinylsiloxy-endblocked polydiorganosiloxane gumconsisting essentially of 99.86 mole percent of dimethylsiloxane unitsand 0.14 mole percent of methylvinylsiloxane units based on the totalmoles of diorganosiloxane units present and having a plasticity (4.2 gsample) in the range of about 1.40-1.65 millimeters (55-65 mils).

"Peroxide A"--2,5-dimethyl-2,5-di(t-butylperoxy)hexane.

The test methods used in the following Examples are as follows:

Water Flotation Test (Hydrophobicity of Fillers)--A sample of the silicafiller to be tested is dried in an oven for 15 minutes at 200° C.Approximately 0.1 g of the dried filler (pulverized to insure that it isfree of large particles) is added to 10 ml water in a vial (1 oz. (30ml) volume). The vial is capped and vigorously shaken for about oneminute. After shaking, the amount of powdered sample that floated on thetop of the water was visually estimated. If all of the dried silicapowder floated at the top, the sample was deemed to possess 100%Hydrophobicity according to the test.

Filler Nonvolatile Solids Content--A sample of filler (10-20 g wet,gelled filler for Examples 1-7, about 2-3 grams for Example 8) isweighed by difference into a weighing dish, dried for 2 hours at 150° C.and reweighed. The final weight divided by the intial weight is reportedas percent nonvolatile solids content.

Treating Agent Level--For purpose of calculation, it is assumed that nomethanol or other volatile materials are lost during the equilibrationstep. The level of filler treating agent desired (based upon the totalweight of the surface-treated filler) is calculated. The amount ofreaction mixture needed to provide the desired weight of a product(nonvolatile surface-treating moeities) consisting of R₂ SiO_(2/2) unitsand RSiO_(3/2) units in the desired ratio is then calculated and thatamount of reaction mixture is used to treat the filler. For example, anequilibrated reaction mixture obtained by equilibrating 136.1 g (1 mole)methyltrimethoxysilane with 74 g (1 mole of (CH₃)₂ SiO_(2/2) units) ofcyclic polysiloxanes of the unit formula [(CH₃)₂ SiO]_(x) where x=3 to 7would have a total weight of 136.1 g+74 g=210.1 g and would provide 67.1g of CH₃ SiO_(3/2) units and 74 g of (CH₃)₂ SiO_(2/2) units for a totalof 141.1 g of nonvolatile surface-treating moeities. Thus, assuming thatthe filler will accept 40 weight percent of surface-treatment moieties,100 g of a silica (SiO₂) filler would require (0.40×100 g)÷0.60=66.7 gof nonvolatile surface treating moieties or (210.1 g×66.7)÷141.1=99.3 gof the equilibrated reaction mixture.

The plasticity of the uncured elastomer formulation or the unfilled gumwas measured using a procedure based on that outlined in ASTM D926. Asample weighing either twice the specific gravity (in grams) of materialcontaining a filler or four times the specific gravity (in grams) ofunfilled gum is cut from the larger mass of material and rolled into aball. The material, in the shape of a ball, was then allowed to age forone hour at 23°±1° C. The sample was then placed between the platens ofa plastometer (Catalog No. C 544445 Parallel Plate Plastometer, ScottTester, Inc., Providence, R.I.) and the upper plate was lowered until itjust touched the top of the sample and was then released withoutdropping it. The plasticity reported is the thickness of the sample 3minutes ±5 seconds after the release of the upper platen when the sampleis at 23°±1° C. The physical properties of the cured and/or post-curedsilicone rubbers were obtained using the following ASTM Methods: ASTMD412--ultimate tensile strength (tensile stress), elongation at breakand modulus (or tensile stress) at 100% elongation: ASTM D624--tear (DieB); and ASTM D2240--durometer. The procedure followed to obtain the hazeand luminous transmittance values is set out in ASTM D1003-61 and weredone on samples that were nominally 1.52 mm (60 mil) thick. Theinstrument used to obtain the values reported in the following exampleswas a Gardner Pivotable Sphere Hazemeter (Model HG 1024) equipped with aModel PG 5500 Digital Photometer (Gardner Laboratory, Bethesda, MD20014). CIE Source C, sometimes called Illuminant C, was used inmeasuring the above values. The haze value reported is percent haze per1.52 mm (60 mil) thickness.

The following examples are intended as being merely illustrative and arenot to be construed as limiting the scope of the present invention tothose examples alone. The scope of the invention is properly defined bythe appended claims. All parts and percentages reported in the followingexamples are by weight unless otherwise indicated.

EXAMPLE 1

This Example demonstrates the preparation of equilibrated reactionmixtures useful in the present invention and their use assurface-treating agents in the preparation of a hydrophobic reinforcingsilica filler. Five mixtures of Mixed Cyclics and methyltrimethoxysilane(MTMS) (see Table I for the reactants) were equilibrated in the presenceof a sufficient amount of Catalyst A to provide 1 potassium atom per1000 silicon atoms (1K/1000Si) present in the mixture.

The equilibration of each mixture was carried out in the absence ofmoisture at 40° C. for a period of 5 days to insure that each mixturewas fully equilibrated (see Example 2 for the type of apparatus used).The composition of each reaction mixture was monitored daily by means ofgas-liquid chromatography. After 5 days, the gas-liquid chromatogramobtained after 4 and 5 days, respectively, for each reaction mixturewere substantially the same and all samples were then deemed to be"equilibrated". Each equilibrated reaction mixture was then cooled toroom temperature. The potassium catalyst was neutralized andprecipitated from the reaction mixture by adding an appropriate amountof dry ice (frozen carbon dioxide) to each reaction mixture. Eachequilibrated reaction mixture was filtered through a bed of perlitefiltering aid supported on a medium porosity glass frit and thefiltrates (Reaction Mixtures A-E, respectively) were stored in theabsence of moisture until each was used to surface treat a silica filleras follows.

A hydrophobic reinforcing silica filler was prepared as described inU.S. Pat. No. 4,344,800 for each Reaction Mixture by first preparing asolution of 7.9 ml methanol, 3.2 ml NH₃ /Methanol Solution and 2.7 mlConc. Ammonium Hydroxide at room temperature. Then, the number of gramsof each Reaction Mixture indicated in Table II was added, with stirring,to that solution. Shortly thereafter, 7.2 ml MOS was added to thestirring mixture. Stirring was continued until the mixture gelled (lessthan 2 minutes) and formed a silica filler-containing composition. Thefiller-containing composition was allowed to age at room temperature.Using the gelation point as the starting point, samples offiller-containing composition were withdrawn at the intervals indicatedin Table II and tested for hydrophobicity using the Water-FlotationTest. The amounts of each Reaction Mixture decrease as the Molar Ratioof R₂ SiO_(2/2) :RSiO_(3/2) increases to obtain a similar level ofsurface-treatment on each sample of filler. The results are reported inTable II. For this series, Reaction Mixtures A and B became 100%hydrophobic in the shortest period of time.

                  TABLE I                                                         ______________________________________                                                                       Molar                                                   Mixed                 Ratio.sup.3                                    Reaction Cyclics      MTMS     Me.sub.2 SiO.sub.2/2 :                         Mixture  g(moles.sup.1)                                                                             g(moles.sup.2)                                                                         MeSiO.sub.3/2                                  ______________________________________                                        A         2.5(0.035)  4.7(0.035)                                                                               1:1                                          B        3.1(0.04)    2.7(0.02)                                                                               2:1                                           C        3.6(0.05)    1.6(0.012)                                                                             4.2:1                                          D        3.6(0.05)    0.9(0.007)                                                                             6.9:1                                          E        3.7(0.05)    0.7(0.005)                                                                              10:1                                          ______________________________________                                         .sup.1 Moles of Me.sub.2 SiO.sub.2/2                                          .sup.2 Moles of MeSiO.sub.3/2                                                 .sup.3 Me.sub.2 SiO.sub.2/2 :MeSiO.sub.3/2                               

                  TABLE II                                                        ______________________________________                                        Run No.     1        2      3      4    5                                     Reaction Mixture                                                                          A        B      C      D    E                                     ______________________________________                                        Amount of Reaction                                                                        3.4      2.9    2.6    2.3  2.2                                   Mixture (g)                                                                   Molar Ratio.sup.2                                                                         1:1      2:1    4.2:1  6.9:1                                                                              10:1                                            % HYDROPHOBICITY                                                    Time (minutes):                                                               15           50      100     40    20   15                                    45          100      100     75    50   25                                    60          100      100     90    80   50                                    120         100      100    100    90   60                                    180         .sup. 100.sup.2                                                                        .sup. 100.sup.2                                                                      100    95   90                                    240         --       --     .sup. 100.sup.2                                                                      98   98                                    300         --       --     --     100  100                                   ______________________________________                                         .sup.1 Ratio of Me.sub.2 SiO.sub.2/2 :MeSiO.sub.3/2                           .sup.2 Filler sample tended to crawl up side of vial                     

EXAMPLE 2

This Example describes the production of hydrophobic reinforcing silicafillers using surface-treating agents derived from reaction mixturesthat were equilibrated with a basic catalyst or with an acidic catalyst.

Reaction Mixture F was prepared in the absence of moisture in a mannersimilar to that employed in Example 1. A higher reaction temperature wasused to reduce the time needed to reach an equilibrated mixture. Thus,544 g of MTMS, 296 g of Mixed Cyclics and 21.6 g of Catalyst A werecombined, with stirring, in a round bottom flask equipped with anair-driven stirrer, water-cooled condenser fitted with a drying tube,thermometer and an addition funnel. After all three components wereadded, the contents of the flask were heated to 100° C., maintained at100° C. for 30 minutes and then cooled to room temperature. As inExample 1, the catalyst was neutralized and the contents were filteredto obtain equilibrated Reaction Mixture F. A gas-liquid chromatogram ofequilibrated Reaction Mixture F showed that it had reached substantiallyan equilibrium level of eluted fractions based upon previous experienceswith reaction mixtures having a molar ratio of Me₂ SiO_(2/2):MeSiO_(3/2) of 1:1.

Reaction Mixture G was prepared using an equilibration procedureemploying an acidic catalyst on a solid resinous support medium. Toremove any free acid that might be present, Catalyst B was thoroughlywashed with methanol until the decanted methanol was neutral when testedwith pH indicator paper. The residual methanol was then removed viavacuum filtration and the Catalyst B was dried for 1 hour at 40° C.before it was used. A vacuum-jacketed, glass column (2 cm innerdiameter) having a stopcock at its lower end was packed with washedbeads of Catalyst B to a depth of 45.7 cm (18 inches) and the bottom ofthe column attached to a 3-liter, round-bottom flask fitted with awater-cooled condenser. A 3-liter, round-bottomed flask having a bottomdrain, an air-powered stirrer, thermometer and water-cooled condenserwas attached to the top of the column by means of the bottom drain. Thetop flask was filled with an equimolar mixture of MTMS and Mixed Cyclicsand the contents were heated to 95° C. with stirring. A sufficientamount of the contents (at 95° C.) was introduced into the catalystcolumn to fill the column and allowed to remain there for 15 minutes towarm the catalyst beads. This was then drained and the remainingcontents of the flask (at 95° C.) was allowed to flow through the columninto the lower flask at the rate of 17 g/minute. A gas-liquidchromatogram of the contents of the lower flask (Reaction Mixture G)showed that the reaction mixture was substantially equilibrated andcontained substantially the same levels of eluted fractions as wereexhibited by Reaction Mixture F.

Hydrophobic reinforcing silica fillers were prepared as in Example 1using the following formulations. Filler F: 82 ml methanol, 31.9 ml NH₃/Methanol Solution, 28.2 ml Conc. Ammonium Hydroxide, 29.65 g ReactionMixture F and 75 ml MOS. The wet, gelled filler composition containingFiller F contained 23.3% nonvolatile solids content and was aged for atleast 24 hours to insure that the filler was adequately surface-treatedbefore it was compounded into a polysiloxane gum (elastomercomposition). Then 66.6 g of the wet, gelled filler compositioncontaining about 15 g Filler F was added to 25 g of Gum A on a two-rollmill without the application of any external heating. After all of thefiller composition was added, the filler-gum base was heated to 120° C.and hot-milled for 15 minutes to remove the volatile portion of thefiller composition. The base was then cooled to room temperature and 13drops of Peroxide A (0.7 parts by weight per 100 parts by weight of GumA) was milled into the base. The catalyzed base was then placed betweentwo sheets of precision calendered polytetrafluoroethylene films in asquare molding chase having polished mold surfaces to prepare a curedelastomer sample with a nominal thickness of 1.52 mm (60 mils). Thechase was placed in a molding press and the catalyzed base was cured for15 minutes at 170° C. followed by a post cure out of the mold for 1 hourat 200° C. The cured elastomer was aged overnight at room temperatureand its physical properties were then tested. Unless otherwiseindicated, this procedure was used to cure and test the compositionsdescribed in this and the following Examples.

A hydrophobic reinforcing silica filler (Filler G) was prepared withReaction Mixture G in place of Reaction Mixture F using the same ratiosof ingredients as described above. The resulting wet, gelled fillercomposition containing Filler G had a nonvolatile solids content of23.0%. The wet, gelled filler composition was aged at least 24 hoursbefore it was compounded into a polysiloxane gum in the same mannerdescribed above using the following formulation: 30 g Gum A, 78.3 g wet,gelled filler composition containing about 18 g Filler G and 17 drops ofPeroxide A. The catalyzed base was cured in the same manner as describedabove.

The filler loading in each sample in parts by weight of filler(nonvolatile solids) per 100 parts by weight of polydiorganosiloxane(hereinafter referred to as "phr") was 62 phr for Run 6 with Filler Fand 60 phr for Run 7 with Filler G. Approximately 40 weight percent ofeach filler was calculated to be contributed by the surface-treatingagent. The physical properties of the cured elastomer are reported inTable III.

                  TABLE III                                                       ______________________________________                                        Run No.                6        7                                             Filler in Sample       Filler F Filler G                                      ______________________________________                                        Physical Properties:                                                          Tensile Strength       12.4/1800                                                                              12.1/1760                                     (MPa/psi).sup.1                                                               Elongation at Break (%)                                                                              630      600                                           Modulus, 100% Elongation                                                                             1.45/210 1.38/200                                      (MPa/psi)                                                                     Durometer (Shore A)    56       56                                            Tear, Die B (kN/m/(ppi)).sup.2                                                                       23.6/135 22.8/130                                      Haze Value             3.1      4.2                                           ______________________________________                                         .sup.1 MPa is megapascals  6.895 MPa = 1000 pounds per square inch (psi)      .sup.2 kN/m is kilonewtons per meter  175 kN/m = 1000 pounds per inch         (ppi)                                                                    

The physical properties for Runs 6 and 7 are quite similar, thus showingthat acid or base catalysis can be employed to obtain the equilibratedreaction mixtures useful in the present invention.

EXAMPLE 3

This Example illustrates the effect of varying the molar ratio of Me₂SiO_(2/2) :MeSiO_(3/2) on the physical properties of the curedelastomers. The Fillers employed in Runs 8 and 9 were prepared using a40 weight percent surface treating agent level for each of the ReactionMixtures shown in Table IV. The same ratios of ingredients were employedto make the wet, gelled fillers used in these Runs as were used inExample 2 for Filler F. Each wet, gelled filler composition was aged for4 hours at room temperature before each was compounded into acomposition curable to an elastomer using the same ratios of ingredientsand curing procedure as described for Example 2 above. The physicalproperties of the cured elastomers are reported in Table IV below. Run10 was prepared in the same manner as were Runs 8 and 9 using thefollowing formulation: 60 ml methanol, 22.6 ml NH₃ /Methanol Solution,20.6 g equilibrated reaction mixture, 20.4 ml Conc. Ammonium Hydroxideand 54 ml MOS. Runs 11 and 12 were the same filler formulations as wereused in Runs 8 and 9, respectively, but the fillers were allowed to age24 hours at room temperature before compounding into elastomers. Run 13employed the same filler ingredient ratios as in Runs 8 and 9, but thefiller was aged overnight (about 16 hours) before it was compounded andcured as in Runs 8 and 9. Aging the fillers enables the fillers tobecome more completely surface-treated and physical properties such ashaze value, tear and elongation at break generally improve with aging ascan be seen from Table IV.

                  TABLE IV                                                        ______________________________________                                        Run No.           8        9        10                                        Equil. Reaction Mixture:                                                      Me.sub.2 SiO.sub.2/2 :MeSiO.sub.3/2                                                             1:1      4:1      10:1                                      Filler Aging Time (hours)                                                                       4        4        4                                         ______________________________________                                        Physical Properties:                                                          Tensile Strength (MPa/psi)                                                                      12.3/1790                                                                              10.2/1480                                                                              7.6/1100                                  Elongation at Break (%)                                                                         540      550      580                                       Modulus, 100% Elong.                                                                            1.65/240 1.52/220 --                                        (MPa/psi)                                                                     Durometer (Shore A)                                                                             60       63       63                                        Tear, Die B (kN/m/(ppi))                                                                        19.8/113 19.3/110 16.8/96                                   Haze Value        4.5      5.3      15.5                                      Plasticity/Recovery                                                                             188/12   212/10   --/--                                     Run No.           11       12       13                                        Equil. Reaction Mixture:                                                      Me.sub.2 SiO.sub.2/2 :MeSiO.sub.3/2                                                             1:1      1:4      1:2.5                                     Filler Aging Time (hours)                                                                       24       24       16                                        ______________________________________                                        Physical Properties:                                                          Tensile Strength (MPa/psi)                                                                      11.2/1620                                                                              11.0/1600                                                                              9.65/1400                                 Elongation at Break (%)                                                                         625      550      680                                       Modulus, 100% Elong.                                                                            1.10/160 1.38/200 1.10/160                                  (MPa/psi)                                                                     Durometer (Shore A)                                                                             53       60       48                                        Tear, Die B (kN/m/(ppi))                                                                        24.5/140 24.8/142 21.8/125                                  Haze Value        1.7      3.7      4.1                                       Plasticity/Recovery                                                                             138/11   197/10   --/--                                     ______________________________________                                    

EXAMPLE 4

This Example describes the use of equilibrated reaction mixturescontaining siloxane units bearing silicon-bonded hydrocarbon radicalssuch as phenyl, vinyl and 3,3,3-trifluoropropyl radicals in addition tomethyl radicals.

Equilibrated Reaction Mixture H was prepared using the apparatusemployed for Reaction Mixture F by equilibrating 74 g of Mixed Cyclics(1 mole of Me₂ SiO_(2/2) units) with a total of 39.4 g (0.2 mole) ofphenyltrimethoxysilane in the presence of 0.09 g of Catalyst C(1K/5000Si). The Mixed Cyclics and one half of thephenyltrimethoxysilane was intially added to a flask and the contentsheated to 120° C. At 120° C., the Catalyst C was added to the contentsand, the reaction mixture was allowed to equilibrate for 45 minutes at120° C. in the presence of the Catalyst C. Then the remainder (19.7 g)of the phenyltrimethoxysilane was added to the mixture and it wasstirred another 45 minutes at 120° C. It was then cooled, neutralizedand filtered as in Example 1 to obtain Reaction Mixture H. ReactionMixture H was used to formulate Filler H according to the proceduredescribed in Example 1 using the following ingredients: 60 ml methanol,22.6 ml NH₃ /Methanol Solution, 20.6 g Reaction Mixture H as asurface-treating agent, 20.4 ml Conc. Ammonium Hydroxide and 54 ml MOS.

Equilibrated Reaction Mixture I was prepared employing the apparatusused for Reaction Mixture F by equilibrating 74 g of Mixed Cyclics witha total of 29.6 g (0.2 moles) vinyltrimethoxysilane. The Mixed Cyclicsand 14.8 g of vinyltrimethoxysilane were mixed together and heated to140° C. 0.09 g (1K/5000Si) of Catalyst C was then added, the mixture wasallowed to equilibrate for 15 minutes at 140° C. and then the remaining14.8 g of vinyltrimethoxysilane was then added. After 30 minutes at 140°C., a gas-liquid chromatogram showed that the reaction mixture wassubstantially equilibrated and the mixture was cooled, neutralized andfiltered as in Example 1 to obtain Reaction Mixture I. Filler I wasprepared in the same manner as Filler H except 22.7 g Reaction Mixture Iwas used as the surface-treating agent in the filler formulation.

Equalibrated Reaction Mixture J was prepared using the apparatus usedfor Reaction Mixture F by heating 74 g Mixed Cyclics and 40.4 g (0.2moles) 3,3,3-trifluoropropyltrimethoxysilane to 110° C. with stirring.Then 0.09 g Catalyst C (1K/5000Si) was added to the mixture and it wasstirred at 110° C. for 20 minutes. At that time, the mixture was foundto be substantially equilibrated via a gas-liquid chromatogram. It wascooled, neutralized and filtered as above to obtain Reaction Mixture J.Filler J was prepared in the same manner as described for Filler H using21.3 g of Reaction Mixture J as the surface-treating agent. Each of thethree wet, gelled filler compositions prepared above were allowed to ageat room temperature for 4 hours (Run Nos. 14, 16 and 18) and for 3 weeks(Run Nos. 15, 17 and 19) after gelation before each was formulated intoan elastomeric composition and cured according to the proceduresdescribed in Example 2. The formulation employed to make eachelastomeric composition was 30 g Gum A, a sufficient amount of a wet,gelled filler composition to provide 18 g of Filler H, I or J and 0.2 g(approximately 12 drops of Peroxide A). Reaction Mixtures H, I and J allhad R₂ SiO_(2/2) :RSiO_(3/2) ratios of 5:1. The physical propertiesobtained for the cured elastomers are reported in Table VI. Table VIindicates that filler aging (i.e., surface-treatment) time appears tohave a significant effect on the optical clarity and tensile strength ofthe cured elastomers.

                                      TABLE VI                                    __________________________________________________________________________    Run No.     14   15   16   17   18   19                                       Filler Type H    H    I    I    J    J                                        Filler Aging Time                                                                         4 hours                                                                            3 weeks                                                                            4 hours                                                                            3 weeks                                                                            4 hours                                                                            3 weeks                                  __________________________________________________________________________    Physical Properties:                                                          Tensile Strength                                                                          12.6/1830                                                                          9.31/1350                                                                          5.86/850                                                                           6.34/920                                                                           9.52/1380                                                                          11.4/1650                                (MPa/psi)                                                                     Elongation at Break (%)                                                                   610  550  50   60   550  550                                      Durometer (Shore A)                                                                       55   52   85   80   65   52                                       Tear, Die B 19.2/110                                                                           20.1/115                                                                           6.1/35                                                                             6.1/35                                                                             28.9/165                                                                           20.1/115                                 (kN/m/(ppi))                                                                  Haze Value  16.3 5.9  5.4  2.3  7.2  3.6                                      Luminous Transmittance                                                                    84.5 90.1 90.5 93.6 91.5 92.9                                     __________________________________________________________________________

Reaction Mixture K was prepared using apparatus similar to that employedfor Reaction Mixture F. A mixture of 136 g (1 mole)methyltrimethoxysilane, 74 g Mixed Cyclics and 3.69 g of1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane (0.048 moles ofMeViSiO_(2/2) where "Vi" is vinyl) was heated to 100° C. with stirring.At 100° C., 5.4 g of Catalyst A (1K/1000Si) was added to the mixture andit was stirred at 95°-100° C. for 45 minutes. The mixture was deemed tobe substantially equilibrated at that point via a gas-liquidchromatogram and the mixture was cooled to 40° C., neutralized andfiltered as above to obtain Reaction Mixture K. Filler K was prepared asabove using the following formulation: 82 ml methanol, 31.9 ml NH₃/Methanol Solution, 28.2 ml Conc. Ammonium Hydroxide, 30.3 g ReactionMixture K as a surface-treating agent and 75 ml MOS. The resulting wet,gelled filler composition (containing filler K) was found to have anonvolatile solids content of 23.0% and had a calculated mole percentageof 2.1% methylvinylsiloxane units. This wet, gelled filler compositionwas used to prepare a cured polydimethylsiloxane silicone elastomerhaving a filler loading level of 60 phr which had a tensile strengthvalue of 10.96 MPa/1590 psi, elongation at break of 917%, modulus at100% elongation of 2.36 MPa/343 psi, durometer (Shore A) of 64, Die Btear value of 42.2 kN/m/(241 ppi), haze value of 1.6% at 1.52 mmthickness and luminous transmittance of 93.2% at 1.52 mm thickness.

Equilibrated Reaction Mixture L was prepared in the same manner as wasReaction Mixture K using 136 g (1 mole) methyltrimethoxysilane, 74 gMixed Cyclics and 6.35 g (0.043 moles) vinyltrimethoxysilane. Filler Mwas prepared using the same procedure employed for Filler K using 30.7 gof Reaction Mixture L employed as the surface-treating agent. Theresulting wet, gelled filler composition (22.9% nonvolatile solidscontent, 2.1 mole % vinylsiloxane units) containing Filler M was used toprepare a cured polydimethylsiloxane silicone elastomer having a fillerloading level of 60 phr which had a tensile strength of 10.57 MPa/1533psi, elongation at break of 787%, modulus at 100% elongation of 2.57MPa/373 psi, durometer (Shore A) of 67, Die B tear of 41.8/kN/m/(239ppi), haze value of 1.3% at 1.52 mm thickness and luminous transmittanceof 93.3%.

EXAMPLE 5

The following wet, gelled filler composition was prepared in the mannerdescribed in Example 1 using the following formulation: 246 ml (194 g)methanol, 96 ml (76.6 g) NH₃ /Methanol Solution, 84.6 ml (75.3 g) Conc.Ammonium Hydroxide, 89 g of an equilibrated reaction mixture having amolar ratio of Me₂ SiO_(2/2) :MeSiO_(3/2) units of 1:1 and 225 ml (228g) MOS. Fillers prepared from equilibrated reaction mixtures of thismolar ratio gave the best overall properties in a cured siliconeelastomer in a reasonably short period of time. To demonstrate the speedat which ultimate physical properties of the cured elastomer aredeveloped, the above wet, gelled filler composition was aged at roomtemperature for 1, 2, 4, 8 and 24 hours after gelation and formulatedinto elastomeric compositions and cured as in Example 2 using thefollowing formulation: 25 g Gum A, 66.4 g of the wet, gelled fillercomposition (15 g nonvolatile solids) and 13.5 drops Peroxide A. Thephysical properties of the cured elastomer are reported in Table VII andthe data obtained indicates that, based upon the physical propertiesobtained, the filler is substantially fully surface-treated after about1 hour of aging time.

                  TABLE VII                                                       ______________________________________                                        Filler     Tensile     Elong.   Modulus,                                      Aging Time Strength    at Break 100% Elong.                                   (hours)    (MPa/psi)   (%)      (MPa/psi)                                     ______________________________________                                        1          11.0/1600   570      1.31/190                                      2          11.0/1590   575      1.31/190                                      4          10.9/1580   630      1.03/150                                      8          11.4/1650   620      1.10/160                                      24         11.4/1660   620      1.24/180                                      ______________________________________                                                  Tear,                                                               Durometer Die B          Haze    Lum.                                         (Shore D) (kN/m/ppi))    Value   Trans.                                       ______________________________________                                        62        22.4/128       3.8     92.4                                         57        22.8/130       2.5     92.8                                         52        24.5/140       1.9     92.9                                         53        21.0/120       1.9     92.5                                         54        21.0/120       2.1     92.4                                         ______________________________________                                    

EXAMPLE 6

This Example illustrates the effect of filler surface treating agentlevel on the physical properties of cured elastomers. The fillers wereprepared as in Example 1 using the ratios of ingredients shown in thefollowing formulation: 109 ml methanol, 42.6 ml NH₃ /Methanol Solution,37.6 ml Conc. Ammonium Hydroxide, X g of equilibrated Reaction Mixtureand 100 ml of MOS. One filler series was run using Reaction Mixture Mwhich had a 1:1 molar ratio of Me₂ SiO_(2/2) :MeSiO_(3/2) wherein X inthe above formulation was 19.7 g, 25.3 g, 31.6 g, 39.4 g and 48.0 g,respectively, to obtain filler surface treating agent levels of 25, 30,35, 40 and 45 weight percent of the total filler nonvolatile content.Likewise, another filler series was run using Reaction Mixture N whichhad a 4:1 molar ratio of Me₂ SiO_(2/2) :MeSiO_(3/2) wherein X in theabove formulation was 15.7 g, 20.1 g, 25.3 g, 31.4 g and 38.3 g,respectively, to obtain filler surface treating agent levels of 25, 30,35, 40 and 45 weight percent of the total filler nonvolatile content.The fillers were then formulated into elastomer compositions using 40 gGum A, 24 g of filler solids based on the calculated amount expected tobe present in the wet, gelled filler compositions assuming 100%conversion to filler and 23 drops of Peroxide A. The fillers were agedfor 4 and 24 hours, respectively, before they were formulated into theabove elastomer compositions and cured as in Example I. The physicalproperties of the cured elastomers are reported in Table VIII forfillers treated with Reaction Mixture M and in Table IX for fillerstreated with Reaction Mixture N.

The general trends observed from Tables VIII and IX are that plasticity,haze value, stress whitening, durometer and modulus values decreasedupon aging while the tensile strength and elongation values increasedupon aging. The fillers treated with Reaction Mixture N in generalshowed a greater variation in properties between 4 and 24 hours of agingtime than did those using Reaction Mixture M indicating that the latterfillers appeared to be reaching an optimum level of surface treatmentearlier than fillers using Reaction Mixture N. The plasticity, stresswhitening, haze value, durometer and modulus values decreased while theelongation values tended to increase as the level of surface treatingagent was increased with an optimum level being about 35-40 weightpercent. As the amount of filler treating level was increased, the easeof milling and handling (indicated by the plasticity and recoveryvalues) was also increased. At a 45% treating agent level, the elastomercompositions began to get sticky. Plasticity values of from 160 to 200mils are considered to be desirable.

                  TABLE VIII                                                      ______________________________________                                                                Elong.                                                      Age Of  Tensile   At    Modulus,                                        Treat Filler  Strength  Break 100% Elong.                                                                            Durometer                              Level.sup.1                                                                         (hours) (MPa/psi) (%)   (MPa/psi)                                                                              (Shore A)                              ______________________________________                                        25%   4       11.9/1720 400   3.0/440  78                                     25%   24      12.2/1770 450   201/300  67                                     30%   4       10.1/1468 430   1.9/280  70                                     30%   24      11.8/1710 500   1.5/220  60                                     35%   4       12.5/1810 560   1.8/230  65                                     35%   24      12.3/1790 560   1.8/260  62                                     40%   4       12.3/1790 540   1.7/240  60                                     40%   24      11.2/1620 625   1.1/160  53                                     45%   4        9.7/1410 590   1.0/150  52                                     45%   24      10.8/1560 580   1.1/160  48                                     ______________________________________                                        Tear,                                                                         Die B                                                                         (kN/m/ Haze    Stress   Plasticity/Recovery (mils)                            (ppi)) Value   Whiten.sup.2                                                                           1 hour                                                                              1 day 1 week                                                                              1 month                             ______________________________________                                        25.9/148                                                                             14.3    130% E   356/34                                                                              343/37                                                                              391/57                                                                              378/56                              24.9/142                                                                             4.6     430% E   310/32                                                                              307/33                                                                              351/42                                                                              350/46                              21.9/125                                                                             5.5     160% E   300/20                                                                              302/18                                                                              351/22                                                                              280/30                              21.0/120                                                                             4.2     300% E   278/26                                                                              278/18                                                                              250/20                                                                              254/25                              31.5/180                                                                             2.8     440% E   240/15                                                                              269/31                                                                              276/25                                                                              255/33                              23.4/134                                                                             4.6     none     227/12                                                                              234/23                                                                              242/18                                                                              228/20                              19.8/133                                                                             4.5     none     188/12                                                                              193/16                                                                              199/12                                                                              204/14                              24.5/140                                                                             1.7     600% E   138/11                                                                              129/10                                                                              147/6 154/9                               19.1/109                                                                             3.0     370% E   102/2 127/9 138/5 140/3                               15.1/86                                                                              3.3     420% E   121/7 99/8  111/2 114/6                               ______________________________________                                         .sup.1 Filler surface treatment level is weight percent of total filler       .sup.2 Stress whitening is the elongation (E) value at which an optically     clear elastomer tensile bar visually becomes whitened and opaque         

                  TABLE IX                                                        ______________________________________                                                      Tensile                                                               Age Of  Strength Elong. Modulus                                         Treat Filler  (MPa/    At Break                                                                             100% Elong.                                                                            Durometer                              Level.sup.1                                                                         (hours) psi)     (%)    (MPa/psi)                                                                              (Shore A)                              ______________________________________                                        25%    4               TOO HARD                                                                      TO COMPOUND                                            25%   24      10.7/1550                                                                              375    3.8/550  81                                     30%    4      11.4/1660                                                                              350    3.4/500  80                                     30%   24      12.4/1800                                                                              500    1.9/280  70                                     35%    4       9.7/1400                                                                              490    2.2/320  74                                     35%   24      12.0/1740                                                                              530    1.7/240  65                                     40%    4      10.2/1480                                                                              550    1.5/220  63                                     40%   24      11.4/1650                                                                              580    1.4/200  61                                     45%    4      10.5/1520                                                                              620    1.6/230  53                                     45%   24      10.7/1550                                                                              600    1.0/140  50                                     ______________________________________                                        Tear,                                                                         Die B                                                                         (kN/m/ Haze    Stress   Plasticity/Recovery (mils)                            (ppi)) Value   Whiten.sup.2                                                                           1 hour                                                                              1 day 1 week                                                                              1 month                             ______________________________________                                        TOO HARD TO COMPOUND                                                          16/92  7.9     350% E   373/41                                                                              434/66                                                                              400/52                                                                              537/95                              16/94  10.4     60% E   360/37                                                                              369/46                                                                              402/50                                                                              468/49                              22.7/130                                                                             2.8     480% E   277/22                                                                              277/31                                                                              305/31                                                                              350/54                              20.1/115                                                                             15.4     55% E   286/19                                                                              282/29                                                                              312/32                                                                              320/25                              20.1/115                                                                             1.8     420% E   229/16                                                                              229/16                                                                              275/28                                                                              254/26                              19.3/110                                                                             5.3     130% E   212/12                                                                              194/14                                                                              216/8 231/10                              17/95  2.7     410% E   181/8 186/15                                                                              200/12                                                                              219/17                              21.9/125                                                                             5.5     140% E   149/10                                                                              133/10                                                                              150/5 177/12                              18.9/108                                                                             2.4     350% E   106/3 97/6  110/3 124/7                               ______________________________________                                         .sup.1 Filler surface treatment level is weight percent of total filler       .sup.2 Stress whitening is the elongation (E) value at which an optically     clear elastomer tensile bar visually becomes whitened and opaque         

EXAMPLE 7

Silicone elastomers containing the surface-treated silica fillers usedin the previous Examples were highly transparent and those having hazevalues of less than 2.4% at 1.52 mm thickness are considered to beoptically clear. A phenomenon referred to as stress whitening wasobserved (see Example 6) when the sample was elongated and this can beof concern if the elastomer is used in an application which requiresthat it have a high degree of clarity. One means for greatly reducing oralleviating this phenomenon was to reduce the level of ammonia used toprepare the fillers when the method described in U.S. Pat. No. 4,344,800was used to prepare the fillers. The previous Examples employed anammonia (NH₃) level of about 0.13 g NH₃ per gram of MOS. It was foundthat the amount of stress whitening could be reduced by decreasing thelevel of ammonia to from 0.093 to 0.0093 g NH₃ per gram of MOS in thefiller formulation.

The basic filler formulation employed was 220 ml methanol, 150 ml of MOSand 59.1 g of an equilibrated Reaction Mixture having a molar ratio ofMe₂ SiO_(2/2) :MeSio_(3/2) of 1:1. The following amounts of Conc.Ammonium Hydroxide and, optionally, water, were used in the above fillerformulation to obtain the indicated ammonia concentration level:

    ______________________________________                                        gNH.sub.3 /g MOS                                                                           Conc. Amm. Hydroxide                                                                          Water                                            ______________________________________                                        0.093        56.4 ml         0                                                0.047        28.2 ml         17.7 ml                                          0.031        18.8 ml         23.8 ml                                          0.023        14.1 ml         26.9 ml                                          0.093         5.6 ml         32.3 ml                                          ______________________________________                                    

In the above formulations, the Conc. Ammonium Hydroxide was added lastin preparing the wet, gelled filler composition. Each filler compositionwas aged for 24 hours at room temperature. Each filler composition wasthen compounded with Gum A at a filler loading level of 60 phr in thesame manner described for the elastomeric compositions employed inExample 6 and cured as in Example 6. The physical properties of thecured elastomers and plasticity/recovery of the uncured compositions arereported in Table X.

For this series, the cured elastomers did not exhibit stress whiteningat or below an ammonia concentration of 0.047 g NH₃ /g MOS. Reducing theammonia concentration also resulted in an increase in tensile strength,modulus, durometer, die B tear values and plasticity.

Samples of the fillers prepared using 0.093 g NH₃ /g MOS and 0.031 g NH₃/g MOS were aged 6 weeks at room temperature before they were compoundedinto elastomers as above. Neither of the cured elastomers prepared fromthese fillers exhibited stress whitening.

                  TABLE X                                                         ______________________________________                                        NH.sub.3 Level                                                                        Tensile             Modulus,                                          (g NH.sub.3 /g                                                                        Strength  Elongation                                                                              100% Elong.                                                                            Durometer                                MOS)    (MPa/psi) (%)       (MPa/psi)                                                                              (Shore A)                                ______________________________________                                        0.13    11.2/1620 625       1.1/160  53                                       0.093   11.4/1650 600       1.2/180  58                                       0.047   11.7/1700 640       1.5/220  59                                       0.031   13.1/1900 610       1.9/280  64                                       0.023   12.7/1840 580       2.1/300  65                                        0.0093 10.3/1500 570       2.3/330  65                                       ______________________________________                                        Tear,                                                                         Die B                                                                         (kN/m/ Haze    Stress   Plasticity/Recovery                                   (ppi)) Value   Whiten.sup.1                                                                           1 hour                                                                              1 day 1 week                                                                              1 month                             ______________________________________                                        24.5/140                                                                             1.7     600% E   138/11                                                                              139/10                                                                              147/16                                                                              154/9                               23.4/134                                                                             1.5     550% E   161/7 155/5 175/9 170/9                               28.7/164                                                                             2.9     none     205/13                                                                              215/13                                                                              217/10                                                                              235/20                              26.8/153                                                                             3.0     none     248/26                                                                              262/29                                                                              257/28                                                                              271/33                              27.0/154                                                                             2.0     none     266/26                                                                              271/29                                                                              273/31                                                                              288/36                              28.4/162                                                                             1.5     none     269/26                                                                              275/30                                                                              284/32                                                                              301/41                              ______________________________________                                         .sup.1 Stress whitening is the elongation (E) value at which an optically     clear elastomer tensile bar visually becomes whitened and opaque         

EXAMPLE 8

This Example demonstrates the use of the equilibrated reaction mixturesof the present invention to surface-treat a preformed, reinforcingsilica filler. That filler (hereinafter "Fume Silica") was reportedlyprepared by the flame hydrolysis of tetrachlorosilane and wascommercially obtained from Cabot Corporation, Boston, MA under thetrademark CAB-O-SIL®MS-75. The manufacturer reports that the surfacearea (BET Method) of that filler was 255±15 square meters per gram.

For comparative purposes, a sample of Fume Silica was surface-treatedwith hexamethyldisilazane (100 parts by weight of filler/30 parts byweight of hexamethyldisilazane) in the presence of a small amount ofwater and that filler was believed to contain about 21 weight percent ofsurface treating agent in the form of Me₃ SiO_(1/2) units (Run No. 20).

Each of the following amounts of an equilibrated reaction mixture havinga molar ratio of Me₂ SiO_(2/2) :MeSiO_(3/2) of 1:1 were tumbled with 40g of Fume Silica in a sealed metal can for about 2.5 days at roomtemperature to obtain a surface-treated silica filler: 8.6 g (Run No.21), 15.4 g (Run No. 22), and 40 g (Run No. 23), respectively. Likewise,11.9 g (Run No. 24) and 31.74 g (Run No. 25), respectively, of anequilibrated reaction mixture having a molar ratio of Me₂ SiO_(2/2):MeSiO_(3/2) of 4:1 were each tumbled overnight at room temperature in asealed metal can with 40 g of Fume Silica to obtain a surface-treatedsilica filler.

To check the effect of a basic catalyst on surface-treatment, thefollowing mixture was tumbled together overnight at room temperature ina sealed metal can to obtain a surface-treated silica filler: 40 g FumeSilica, 31.74 g of the above 1:4 molar ratio Reaction Mixture and 2.6 gammonium carbonate (Run No. 26). To determine the fillersurface-treatment level of the fillers, the fillers were placed in anoven for 2 hours at 150° C. and the weight loss on heating wascalculated. Since the metal cans were sealed, the loss in weight uponheating was attributed to filler surface-treatment loss and the amountof filler surface-treatment levels reported in Table XI were calculatedfrom this weight loss.

Another sample of Fume Silica was surface-treated (Run No. 27) bytumbling a mixture of 15 g Fume Silica, 15 g of an equilibrated reactionmixture having a molar ratio of Me₂ SiO_(2/2) :MeSiO_(3/2) of 1:1, 55 gmethanol and 2 g Conc. Ammonium Hydroxide.

Each of the above fillers was compounded into elastomeric compositionswith Gum A at a filler loading level (filler nonvolatile solids) of 50phr. The elastomer composition was catalyzed with 0.7 phr of Peroxide Aand cured as in Example 2. The physical properties of the curedelastomers are reported in Table XI beside the headings Run Nos. 20 to27.

Finally, the use of an equilibrated reaction mixture having a molarratio of Me₂ SiO_(2/2) :MeSiO_(3/2) of 1:1 was employed as a plasticizerfor a mixture of Fume Silica and Gum A. Two elastomeric compositionswere prepared. Run No. 28 had the following formulation: 25 g Gum A, 10g Fume Silica, 3.75 g (2.5 g nonvolatile treating agent) of the 1:1molar ratio reaction mixture and 0.175 g Peroxide A. Run No. 29 had thefollowing formulation: 25 g Gum A, 7.5 g Fume Silica, 7.5 g (5 gnonvolatile treating agent) and 0.175 g Peroxide A. Each formulation wascalculated to have 12.5 g filler nonvolatile solids with the filler usedin Run 29 having a filler surface treatment level (40 weight percent)twice that of the filler of Run 28 (20 weight percent). The Gum A wasplaced on a two-roll mill, one-fourth of the Fume Silica was blendedinto the gum followed by one-fourth of the reaction mixture. Thisprocess was repeated three more times. After all the silica and reactionmixture was added, the mixture was milled 10 minutes at 110° C., cooledto room temperature and the Peroxide A was milled into the mixture. Eachformulation was, then cured as in Example 2 and the physical propertiesobtained are reported in Table XI.

Run Nos. 21-23 gave lower haze values than the other Run Nos. 20 and24-29, had better uncured plasticity values than Run No. 20, and had thehighest tear values of this series of Runs. The properties obtained withRun 29 were comparable to that obtained for comparative Run No. 20.

                  TABLE XI                                                        ______________________________________                                              Surface                                                                       Treatment Tensile           Modulus,                                    Run   Level     Strength  Elongation                                                                            100% Elongation                             No.   (wt. %)   (MPa/psi) (%)     (MPa/psi)                                   ______________________________________                                        20    21        9.24/1340 550     0.8/120                                     21    9.5       10.3/1500 460     1.2/180                                     22    12.4      11.2/1630 490     1.4/210                                     23    18.7      8.3/1200  700     0.7/100                                     24    12.6      9.1/1320  470     1.2/175                                     25    30.3      9.2/1330  640     0.8/120                                     26    24        9.6/1390  840     0.6/80                                      27    --        9.5/1375  750     0.6/80                                      28    --        9.5/1375  415     1.1/160                                     29    --        7.6/1100  530     0.8/120                                     ______________________________________                                                            Tear,      Haze  Plasticity/                                       Durometer  Die B      Value Recovery                                 Run No.  (Shore A)  (kN/m/ppi))                                                                              (%)   (mils)                                   ______________________________________                                        20       41         10.9/62    21.8  73/6                                     21       58         14.4/82    12.5  126/2                                    22       54          20.3/116  11.6  109/4                                    23       46          26.8/153  13.6  91/4                                     24       58         11.9/68    24.5  90/5                                     25       45         12.6/72    22.6  72/4                                     26       36          17.5/100  33.1  65/5                                     27       37          9.6/55    19.4  --                                       28       57         10.0/57    18.5  --                                       29       46         10.2/58    20.9  --                                       ______________________________________                                    

That which is claimed is:
 1. A method of surface treating a particulate inorganic filler which comprises the steps of(A) contacting 100 parts by weight of a particulate inorganic filler with a surface treating agent comprising at least one component which is an equilibrated reaction mixture consisting essentially of R₂ SiO_(2/2) units, RSiO_(3/2) units and CH₃ O_(1/2) radicals, there being A moles of R₂ SiO_(2/2) units per mole of RSiO_(3/2) units present in said mixture and B moles of said CH₃ O_(1/2) radicals, said A having an average value of from 0.5 to 10 and B having an average value of from 3 to 6, the value of B being related to A such that when A=0.5, B=6 and when A=10, B=3, and wherein R is selected from the group consisting of hydrocarbon radicals of from 1 to 10 inclusive carbon atoms and haloalkyl radicals of from 1 to 10 inclusive carbon atoms, said reaction mixture (1) having been prepared by equilibration in the presence of a catalyst for the equilibration reaction and (2) having an overall average molecular weight of less than 500, there being at least 5 and up to 50 parts of weight of said equilibrated reaction mixture based on the total weight of R₂ SiO_(2/2) and RSiO_(3/2) units present in the mixture per 100 parts by weight of said filler, and (B) maintaining said surface-treating agent in contact with said filler for a sufficient amount of time to obtain a hydrophobic, surface-treated particulate inorganic filler.
 2. The method as claimed in claim 1 wherein said reaction mixture is obtained by equilibrating a mixture of (1) cyclic polydiorganosiloxanes of the average formula (R₂ SIO)_(x) and (2) RSi(OCH₃)₃ wherein the amounts of (1) and (2) are selected such that the equilibrated reaction mixture has a molar ratio of R₂ SiO_(2/2) :RSiO_(3/2) units in the range of 0.5:1 to 10:1, said x having an average value of from 3 to
 7. 3. The method as claimed in claim 2 wherein the inorganic filler is a silica filler having a surface area of at least 50 m² /g, the ratio of R₂ SiO_(2/2) :RSiO_(3/2) is in the range of 0.75:1 to 4:1 and at least 70 weight percent of the cyclic polysiloxanes are cyclic polysiloxanes wherein x=4, and wherein more than 50 mole percent of the total moles of R radicals present in said reaction mixture are methyl radicals.
 4. The method as claimed in claim 3 wherein R is selected from the group consisting of methyl and vinyl radicals, no more than 10 mole percent of the total moles of R radicals present in said reaction mixture being vinyl radicals.
 5. The method as claimed in claim 3 wherein the ratio of R₂ SiO_(2/2) :RSiO_(3/2) is in the range of 0.9:1 to 1.1:1.
 6. The method as claimed in claim 5 wherein R is selected from the group consisting of methyl and vinyl radicals, no more than 10 mole percent of the total moles of R radicals present in said reaction mixture being vinyl radicals.
 7. A hydrophobic, surface-treated particulate inorganic filler which has been surface treated in accordance with the method of claim
 1. 8. A hydrophobic, surface-treated particulate inorganic filler which has been surface treated in accordance with the method of claim
 2. 9. A hydrophobic, surface-treated particulate silica filler which has been surface treated in accordance with the method of claim
 3. 10. A hydrophobic, surface-treated particulate silica filler which has been surface treated in accordance with the method of claim
 4. 11. A hydrophobic, surface-treated particulate silica filler which has been surface treated in accordance with method of claim
 5. 12. A hydrophobic, surface treated particulate silica filler which has been surface treated in accordance with the method of claim
 6. 13. A composition curable to a silicone elastomer comprising from 50 to 97.5 parts by weight of at least one polydiorganosiloxane and from 2.5 to 50 parts by weight of a particulate inorganic filler which has been surface treated in accordance with the method of claim
 1. 14. The curable composition as claimed in claim 13 wherein said reaction mixture is obtained by equilibrating a mixture of (1) cyclic polydiorganosiloxanes of the average formula (R₂ SiO)_(x) and (2) RSi(OCH₃)₃ wherein the amount of (1) and (2) are selected such that the equilibrated reaction mixture has a molar ratio of R₂ SiO_(2/2) :RSiO_(3/2) units in the range of 0.5:1 to 10:1.
 15. The curable composition as claimed in claim 14 wherein the inorganic filler is a silica filler having a surface area of at least 50 m² /g, the ratio of R₂ SiO_(2/2) :RSiO_(3/2) is in the range of 0.75:1 to 4:1 and at least 70 weight percent of the cyclic polysiloxanes are cyclic polysiloxanes wherein x=4.
 16. The curable composition as claimed in claim 15 wherein R is selected from the group consisting of methyl and vinyl radicals, no more then 10 mole percent of the total moles of R radicals present in said reaction mixture being vinyl radicals.
 17. The curable composition as claimed in claim 16 wherein the ratio of R₂ SiO_(2/2) :RSiO_(3/2) is in the range of 0.9:1 to 1.1:1.
 18. The curable composition as claimed in claim 17 wherein R is selected from the group consisting of methyl and vinyl radicals, no more than 10 mole percent of the total moles of R radicals present in said reaction mixture being vinyl radicals.
 19. A cured elastomer comprising the product obtained upon curing the composition of claim
 13. 20. A cured elastomer comprising the product obtained upon curing the composition of claim
 14. 21. A cured elastomer comprising the product obtained upon curing the composition of claim
 15. 22. A cured elastomer comprising the product obtained upon curing the composition of claim
 17. 23. A cured elastomer comprising the product obtained upon curing the composition of claim
 18. 24. The cured elastomer of claim 20 which is in the form of a prosthetic device.
 25. The cured elastomer of claim 21 which is in the form of a prosthetic device.
 26. The cured elastomer of claim 22 which is in the form of a prosthetic device.
 27. The cured elastomer of claim 23 which is in the form of a prosthetic device. 